Power sub-frame for a system unit

ABSTRACT

A power sub-frame is provided for a system unit. The power sub-frame has four walls defining first, second, third and fourth sides of a open, rectangular frame. A fifth side is open for receiving a plurality of power supply units for powering the system unit. A power distribution board located at a sixth side of the frame opposite to the open side, for making electrical contact to the power supply units. The power sub-frame can be manufactured as a sub-assembly for the system unit, facilitating manufacture, testing and maintenance. The power sub-frame can be pre-assembled with power distribution logic and cabling ready to be mounted in a system unit. The system unit can, for example, be a computer system unit for rack mounting in a telecommunications application.

BACKGROUND OF THE INVENTION

The invention relates to powering system units. In particular, theinvention relates to facilitating the manufacture and maintenance ofsystem units that require a reliable power supply for use inenvironments and applications that place high demands on systemreliability, for example in the telecommunications industry.

Deregulation and privatization is causing unprecedented competition inthe worldwide telecommunications market. This climate of fiercecompetition has meant that service providers must introduce new, moresophisticated and user-friendly services at an accelerated pace toretain or attract subscribers, while not compromising traditionaltelecommunications company (telco) service quality.

These pressures of competition have also placed high demands on NetworkEquipment Providers (NEPs). Traditionally, NEPs have designed, built andsupported proprietary computing equipment, as the strict telcorequirements could not be met by the commercial computing sector. Thoserequirements include the so-called Telcordia Technologies NetworkEquipment Buildings Systems (NEBS) tests. However, due to the lead timesrequired to design and test such proprietary equipment, and the cost ofsupporting such equipment, there is a need to find another route, atleast for the supply of the more cost and performance sensitive sectorswithin the telco industry.

A major concern of the telco sector is the reliability of systems. Toaddress this issue, many prior systems, for example for providing thefunction of a telco server computer, have employed redundant computersystems. In such a redundant computer system, two or more processingsets are provided, typically with each being configured on a separatemotherboard and with a mechanism for voting between the processing setsto determine whether one is faulty. Each of the processing sets mayinclude one or more processors. If the voting system determines that oneof the processing sets is faulty, then the other one or more processingsets can continue to function. In such systems, other multiple versionsof other of the components of the system can be provided. For example,it is known to provide three power supply units such that if one of thepower supply units fails, the system can continue to function with powerfrom the remaining two power supply units.

In order to keep up with the ever-increasing demands of the telcoindustry, and in order to provide equipment at reasonable cost andwithin reasonable time scales, it would be desirable facilitatemanufacture and testing of the system units and components. Also, inorder to reduce as far as possible any down time, it is desirable thatmaintenance is facilitated.

Accordingly, it is an aim of the present invention to address theprovision of cost-effective equipment that can meet technical demands ofthe telco environments, while also meeting the modern commercial demandsof that environment.

SUMMARY OF THE INVENTION

Particular and preferred aspects of the invention are set out in theaccompanying independent and dependent claims. Combinations of featuresfrom the dependent claims may be combined with features of theindependent claims as appropriate and not merely as explicitly set outin the claims.

In accordance with one aspect of the invention, there is provided apower sub-frame for a system unit. The power sub-frame comprises fourwalls defining first, second, third and fourth sides of a rectangularframe, a fifth, open, side of the frame for receiving a plurality ofpower supply units for powering the system unit and a power distributionboard located at a sixth side of the frame opposite to the open side formaking electrical contact to the power supply units.

The power subframe can be manufactured as a sub-assembly for the systemunit, facilitating manufacture. This can be tested separately prior toinsertion in the system unit, to enhance reliability. Also, the powersub-frame can be configured as a field replaceable unit, facilitatingmaintenance and reducing maintenance times.

To facilitate the mounting of the power supply units, internal walls canbe provided for defining a plurality of compartments, each for receivinga power supply unit. In one embodiment there are two internal walls fordefining three compartments.

The power sub-frame can include formations for securing the powersub-frame in the system unit. In one embodiment, these formations areformed by flanges with holes for receiving retaining screws.

To further facilitate assembly, testing and maintenance, the powerdistribution board can be pre-assembled with cabling for connection tocomponents of the system unit.

Moreover, to yet further facilitate assembly, testing and maintenance,the power distribution board can be provided with power distributionlogic. The power distribution board can also be arranged to carry aplurality of power rails for supplying different components. In thismanner, good insulation against electrical noise between power rails canbe provided.

In an embodiment of the invention, the walls of the power sub-frame canbe stamped and folded from metal sheet.

In another aspect of the invention, there is provided a system unitcomprising electronic circuitry and power sub-assembly, the powersub-assembly being formed by a power sub-frame including four wallsdefining first, second, third and fourth sides of a rectangular frame, afifth, open, side of the frame for receiving a plurality of power supplyunits for powering the system unit and a power distribution boardlocated at a sixth side of the frame opposite to the open side formaking electrical contact to the power supply units.

In a further aspect of the invention, there is provided a method ofassembling a system unit including a plurality of power supply units,the method comprising: providing a sub-assembly forming a powersub-frame, the power sub-frame comprising four walls defining first,second, third and fourth sides of a rectangular frame, a fifth, openside of the frame for receiving a plurality of power supply units forpowering the system unit and a power distribution board located at asixth side of the frame opposite to the open side for making electricalcontact to the power supply units; and mounting the power sub-framesub-assembly in the system unit.

The system unit can be a computer system unit for mounting in a rack.Thus, an embodiment of the invention can facilitate manufacture, testingand maintenance of a computer system unit for use in environments thatplace high demands on cost, reliability and ease of maintenance toreduce potential down times. Accordingly, an embodiment of the inventionis ideally suited to telecommunications applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be describedhereinafter, by way of example only, with reference to the accompanyingdrawings in which like reference signs relate to like elements and inwhich:

FIG. 1 is a perspective view from the front of an embodiment of theinvention including sacrificial transport brackets;

FIGS. 2A and 2B are plan and front views, respectively of the embodimentof FIG. 1 with alternative mounting brackets, and

FIG. 2C is a side view showing the mounting holes for alternative typesof mounting arrangements;

FIG. 3 is perspective view from the rear of the embodiment FIGS. 1 and 2illustrating a removable top cover;

FIG. 4 is an exploded view of the aforementioned embodiment;

FIG. 5 is a front view of the aforementioned embodiment;

FIG. 6 is a rear view of the aforementioned embodiment;

FIG. 7 is a plan view of a computer motherboard;

FIG. 8 is schematic block diagram of and example of the architecture ofan embodiment of the invention;

FIG. 9 is perspective view from the rear of the embodiment FIGS. 1 and 2illustrating the removal of a power supply unit;

FIGS. 10A, 10B, 10C and 10D are rear, top, front and perspective viewsof a power sub-frame for receiving three power supply unit, and

FIG. 10E illustrates connections for various connectors of a powersub-frame assembly;

FIG. 11 is a schematic diagram of circuitry from a power distributionboard of the power sub-frame of FIG. 10;

FIG. 12 illustrates the location of an alarm circuit;

FIG. 13 is a schematic block diagram of the logic of the alarm circuit;and

FIG. 14 is a schematic diagram illustrating the configuration of a fancontrol module.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, a particular embodiment of the invention will bedescribed by way of example only.

FIG. 1 is a perspective view of a system unit 10 for use in arack-mountable system. In a particular example described herein, thesystem unit is a computer system unit for forming a computer server fora telecommunications application, for example an Internet server. Asshown in FIG. 1, the unit 10 has a front surface 12 formed by a frontwall, a rear surface 14 formed by a rear wall, a left end surface 16formed by a left side wall, a right end surface 18 formed by a rightside wall, a lower surface 20 formed by a base wall and an upper surface22, in the present example formed by a cover 30. As shown in FIG. 1, thesystem unit 10 is provided with sacrificial transport flanges 24, whichextend above and below the system unit. This optional feature is removedbefore installation of the system unit 10 in a rack.

The system unit 10 is constructed with an extremely robust chassis 11,with the various walls 12-20 and the cover 30 forming the casing of thechassis 11 as well as internal walls (not shown) being formed of heavygauge steel. The walls of the chassis can be made, for example, fromelectroless nickel-plated mild steel with a thickness of, for example,1.5 to 2.0-mm.

The steel chassis 11 is pre-formed with mounting holes for theattachment of mounting flanges or a slide mechanism to enable the systemunit 10 to be provided with a wide variety of mounting options and racksizes. Mounting flanges can be provided to suit standard 19-inch,23-inch, 24-inch or 600-mm nominal frame widths. (One inch=approximately25.4 mm).

FIG. 2A is a plan view of the unit 10 showing the upper surface 22/cover30 and various options for flanges 26 with the displacements from thefront surface indicated in mm.

FIG. 2B is a front view of the unit 10 showing the front surface 12 andtwo different examples of mounting flanges 26. The mounting flange shownto the left (as seen in FIG. 2B) is provided with a handle to facilitateinsertion and removal of the unit 10 from the racking system, whereasthe flange 26 to the right (as viewed in FIG. 2B) is not provided with ahandle.

In the present example, the mounting flanges can be attached usingscrews which pass through the mounting flange into threaded holes in theend walls 14, 16 at either side of the chassis 11 of the unit 10. FIG.2C is a side view of the system unit 10, showing the holes in the sideof the system unit 10 for the mounting of flanges or a slide mechanism.Vertical rows of holes are for the attachment of flanges to be attachedto vertical rack components, and horizontal rows of holes provide forthe attachment of a runners for permitting a slideable mounting of thesystem unit in a rack.

FIG. 3 is a perspective rear view of the unit 10 showing the cover 30that forms the top surface 22 of the unit 10 As can be seen, the cover30 is provided with front locating flanges 32 that, in use, engage aco-operating front flange 31 of the body of the chassis 11. Side flanges33 engage either side of the end walls forming the left and right ends16 and 18 of the chassis 11. Detents 34 on those end walls engage withinL-shaped slots 35 in the side flanges 33 so that the cover may belowered onto the top of the chassis 11 and then moved forwards so as tocause the detents 34 to latch within the slots 35. At the rear of thecover 30, a rear flange 36 with a lower lip 37 engages over an abutment38 at the top of the rear end wall 14 of the casing 10. The cover can besecured to the remainder of the chassis 11 by means of a screw 39 thatpasses through this rear flange into a threaded hole in the abutment 38.

FIG. 4 is an exploded perspective view from the front of the system unit10. This shows a motherboard 40 that is mounted on a horizontal mountingplane 41 within the chassis 11. Mounted on the motherboard 40 arebetween one and four processor modules 42. A riser card 44 can receive aplurality of dual in-line memory modules (DIMMs) 46. Further DIMMs 46can be received directly in slots in the motherboard. A slideablecarriage 48 is provided for receiving one or more media drives.

As shown in FIG. 4, the slideable carriage 48 can receive up to twomedia drives. In the present instance, two media drives including adigital audio tape (DAT) drive 50 and a CD-ROM drive 52 are provided.Appropriately configured metal cover plates 54 and 56 are provided forthe media drives 50 and 52. A disc bay assembly 58 provides a smallcomputer system interface (SCSI) backplane and cables for receiving oneor more SCSI media drives, such as a SCSI disc drive 60. Although, inthe present instance, the drives are controlled via a SCSI-typeinterface, it will be appreciated that another media drive interface(e.g., IDE) could be used. A SCSI card (not shown) is located within thechassis to the front of the motherboard. A bezel (decor panel) 62 isprovided for covering ventilation holes 63 in the front wall 12 of thechassis 11. A bezel 64 is provided for covering the media drives 50, 52and 60.

A fan control module 66 controls the operation of processor fans 68 andsystem fans 70. A power sub-assembly that includes a power sub-frame 72with a power distribution board assembly, is provided for receivingthree separate power supply units 74. An alarms module in the form of analarms card 78 enables the signalling of alarms to the outside world,and is also connected to an LED card 2 for signalling alarms locally onthe front of the unit 10. A power switch 82 is also provided on thefront surface of the unit 10. FIG. 4 also illustrates one PCI card 84 tobe received within a PCI slot 85 on the motherboard 40.

FIG. 5 is a front view of the unit 10 showing the bezels 62 and 64, apower and alarm panel 90 which includes the power switch 82 and a numberof status light emitting diodes (LEDs) 92. FIG. 5 also illustrates theslots 86 and 88 for the media drives such as media drives 50 and 52shown in FIG. 4.

FIG. 6 is a rear view of the unit 10 in a configuration with three DCpower supply units 74A, 74B and 74C. Each of the power supply units 74A,74B and 74C is the same, and provides redundant power for the unit 10.However, as will be seen later, one or more of the DC power supply unitscould be replaced by AC (mains) power supply units. The power suppliesare hot swappable (i.e., while the system is running), as long as theyare swapped one at a time.

With regard to power supply unit 74A, it can be seen that this isprovided with a handle 94 that is used for inserting and removing thepower supply unit 74A. The handle 94 includes a flange portion that isable to receive a screw 95 for securing the power supply unit to thechassis 11. First and second power cable sockets 96 and 98 are shown.

Also shown is a grounding plate 100 that is secured by knurled nuts 102,104 and 106 to grounding studs 103, 105 and 107. Grounding stud 103provides a connection directly to the chassis 11 of the unit 10.Grounding studs 105 and 107, on the other hand are electrically isolatedfrom the chassis by an insulating board and are instead connected tologic ground (i.e. the ground of the electronic circuitry). By means ofthe grounding plate 100, logic ground can be connected directly tochassis ground. The provision of this grounding plate provides foroptional tying of logic ground to chassis ground. It will be noted thateach of the power supply units 74 is provided with a similar groundingplate 100, for connection to corresponding grounding studs. If it isdesired to isolate logic ground from chassis ground, it is necessary toremove the grounding plate 100 from each of the power supply units 74A,74B and 74C.

An isolated ground system is needed in some telco applications whenoperating in a Regional Bell Operating Company (RBOC) mode. Whenoperating in such a mode, the chassis and logic ground are connected ata remote location to provide, for example, lightning protection. In thiscase two-hole lugs 101 having a pair of holes 111 to fit over the pairof grounding studs 105 and 107 are provided for each of the power supplyunits 74 and are secured over the studs using nuts 104 and 106. Asimilar two-hole lug 101 is secured to the grounding studs 108 and issecured with similar nuts. Earthing wires 109 from each of the two-holelugs 101 on the power units and the chassis then are taken to theremote, earthing location. The studs 103 105, 107 and 108 are of astandard thread size (M5). The studs 105/107 and the studs 108 are at astandard separation (15.85 mm). The studs 105/107 are selfretaining inthe insulated board on the power supply units. The stud 103 isself-retaining in the casing of its power supply unit 74. The suds 108are also self-retaining in the system unit chassis.

In a non-isolated ground situation, chassis ground can simply be tied toa desired ground potential (for example, to the racking system) byconnecting a grounding cable to grounding studs 108 provided on the rearof the chassis. A further earth connection is provided via the powercables for the power supplies.

FIG. 6 also illustrates rear ventilation holes 110 through which air isvented from the system. FIG. 6 also shows the alarms module 78 with aserial connector 112 enabling connection of the alarms module to anetwork for the communication of faults and/or for diagnostic operationson the unit 10 to be performed from a remote location. FIG. 6 also showsa number of PCI cards 84 received within respective PCI slots 116. Anumber of further external connections 114 are provided for connectionof serial connections, parallel connections and SCSI connections, andfor the connection of a keyboard or a Twisted-Pair Ethernet (TPE)connector.

FIG. 7 is a plan view of the motherboard 40 shown in FIG. 4. Four CPUmodule slots 120 are provided. Each of these slots is able to receiveone processor module 42, and any number between one and four slots maybe occupied by a processor module 42. A connector arrangement 122 isprovided for receiving a riser card 44 as shown in FIG. 4. Also,connectors 124 (in four banks) are provided for receiving DIMMs 46 asmentioned with reference to FIG. 4. Edge connectors 126 are provided forconnecting the motherboard to connectors mounted on the mounting plane41. Also shown in FIG. 7 is the slot 128 for the alarms module 78 andvarious ports 130 for the connectors 114 shown in FIG. 6.

FIG. 8 is a schematic overview of the computer architecture of thesystem 10. As shown in FIG. 8, various components within the system areimplemented through application-specific integrated circuits (ASICs).The system is based round a UltraSparc Port Architecture (UPA) bussystem that uses a Peripheral Component Interconnect (PCI) protocol foran I/O expansion bus. The CPU modules 40.0, 40.1, 40.2, 40.3, and aUPA-TO-PCI (U2P) ASIC 154 communicate with each other using the UPAprotocol. The CPU modules 40 and the U2P ASIC 154 are configured as UPAmaster-slave devices. An Address Router (AR) ASIC 154 routes UPA requestpackets through the UPA address bus and controls the flow of data to andfrom memory 150 using a Data Router (DR) ASIC 144 and a switchingnetwork 148. The AR ASIC 154 provides system control. It controls theUPA interconnect between the major system components and main memory.

The DR ASIC 144 is a buffered memory crossbar device that acts as abridge between six system unit buses. The six system unit buses includetwo processor buses, a memory data bus and to I/O buses. The DR ASIC 144provides crossbar functions, memory port decoupling, burst transfer andFirst-in-First-Out (FIFO) data read functions. Clock control for theoperation of the processor is provided by a Reset, Interrupt, Scan andClock (RISC) ASIC 152.

The PCI bus is a high performance 32-bit or 64-bit bus with multiplexedaddress and data lines. The PCI bus provides electrical interconnectionbetween highly integrated peripheral controller components, peripheraladd-on devices, and the processor-memory system. A one-slot PCI bus 155connects to a PCI device 156.0. A three-slot PCI bus connects to threePCI slots 156.1, 156.2 and 156.3. Two controllers are also connected tothe second PCI bus 157. These include a SCSI controller 174 and aPCI-T0-EBus/Ethernet controller (PCIO) 158. The SCSI controller 174provides electrical connection between the motherboard and separateinternal and external SCSI buses. The controller also provides for SCSIbus control. The PCIO 158 connects the PCI bus to the EBus. This enablescommunication between the PCI bus and all miscellaneous I/O functions aswell as the connection to slower, on board functions. Thus, the PCIOenables the connection to an Ethernet connection via a Transmit/Receive(Tx/Rx) module 161 and a network device (ND) module 162

An EBus2 159 provides a connection to various I/O devices and internalcomponents. Super I/O 164 is a commercial off-the-shelf component thatcontains two serial port controllers for keyboard and mouse, an IEEE1284 parallel port interface and an IDE disk interface. The super I/Odrives the various ports directly with some electromagnetic interferencefiltering on the keyboard and parallel port signals. The alarms module78 interfaces with the motherboard and provides various alarm functions.The NVRAM/TOD 168 provides non-volatile read only memory and the time ofday function. Serial port 170 provides a variety of functions. Modemconnection to the serial port 170 enables access to the Internet.Synchronous X.25 modems can be used for telecommunications in Europe. AnASCII text window is accessible through the serial port on non-graphicssystems. Low speed printers, button boxes (for computer aided designapplications) and devices that function like a mouse are also accessiblethrough the serial port. The serial port includes a serial portcontroller, line drivers and line receivers. A one-Mbyte flashprogrammable read only memory (PROM) 172 provides read only memory forthe system.

FIG. 9 is a perspective rear view of the system 10 showing thewithdrawal and/or insertion of a power supply unit 74 in a non-isolatedground situation. In this example, AC power supply units 74 are shown.It can be seen that the power supply unit 74 is provided with the handle94. As shown in FIG. 9, the handle 94 is provided with a grip 184, apivot 182 and a latch 180. To insert the power supply unit 74 it isnecessary to slide the power supply unit into the power sub-frame 72with the grip 184 of the handle 94 slightly raised so that the detent180 can be received under the top 184 of the power sub-frame 72. As thepower supply unit 74 reaches the end of its movement into the powersub-frame 72, connectors (not shown) provided on the power supply unit74 make connection with a corresponding connector on the powerdistribution board at the rear of the power sub-frame 72. Also, at thistime, the handle can be pushed down into the position shown in FIG. 9.This causes the detent 180 to latch behind the upper portion 184 of thepower sub-frame 72. The handle 94 can then be secured in place bytightening the screw 95. The AC power supply unit 74 shown in FIG. 9 hasa single power socket 97, whereas the DC power supply units 74 shown inFIG. 6 have two power sockets 96 and 98. Irrespective of whether thearrangement is as shown in FIG. 6 with two DC power sockets 96 and 98,or as shown in FIG. 9 with one AC power socket 97, the configuration ofthe power socket(s) and the lever 94 is such that the lever cannot bemoved, and therefore the power supply unit cannot be released from thepower sub-frame 72 and the chassis 11 with a plug 186 of a power cable188 in place in one of the power sockets 96/97/98. The removal operationis achieved by releasing the screw 95, removing the power plug, andlifting and pulling on the handle 94.

In an isolated ground situation, in order to hot-swap a power supplyunit 74, it is merely necessary to remove the two-hole lug 101 with itsconnecting earth wire 109 from the studs 105, 107 of the power supplyunit to be removed, to remove the old power supply unit 74, to replace anew power supply unit 74 and then to reconnect the two-hole lug 101 andconnecting earth wire 109 to the studs 105, 107 of the new power supplyunit 74. These operations can all be performed with the system underpower from the other power supply units 74 and with the two-hole lugs101 and earth wires 109 in place over the chassis studs 108 and thestuds 105, 107 of the other power supply units 74.

The isolated ground situation is not shown in FIGS. 6 and 9. In thenon-isolated ground situation shown in FIGS. 6 and 9, hot-swapping of apower supply unit is even easier, as it is merely necessary to removethe selected power supply unit 74 and to replace it with the new powersupply unit 74.

FIGS. 10A, 10B, 10C and 10D are rear, top, front and perspective viewsof a power sub-frame for receiving three power supply units:

The power sub-frame 72 comprises a rectangular, box-shaped frame 191,with four exterior walls on four sides (the top, bottom and two lateralsurfaces), one open side 195 for receiving three power supply units anda power distribution circuit board 190 opposite to the open side. In thepresent instance, the walls are made of electroless nickel-plated mildsteel.

FIG. 10A shows the power distribution board at the “rear” of the powersub-frame (i.e. opposite to the open side). When inserted in the chassisof the system unit, this “rear” of the power sub-frame is actually theforward-most side of the power sub-frame when viewed with respect to thesystem unit. The power distribution board 190 is formed with ventilationholes 194 and carries circuit tracks and components (not shown). FIG.10A also illustrates the flanges 198 with screw holes 199 for securingthe power sub-frame to the rear chassis wall.

FIG. 10B shows the top of power sub-frame. It will be noted that thepower sub-frame body 196 is provided with apertures 197 for lightnessand for ventilation purposes.

FIG. 10C shows the open (front) side 195 (see FIG. 10B) of the powersub-frame. When inserted in the chassis of the system unit, this “front”of the power sub-frame is actually the rear-most side of the powersub-frame when viewed with respect to the system unit. Within the powersub-frame 72, connectors 192A, 192B and 192C for the three power supplyunits 74A, 74B and 74C, respectively, can be seen. These connectors aremounted on the power distribution board 190 inside the power sub-frame72. FIG. 10C also shows the flanges 198 with screw holes 199 forsecuring the power sub-frame to the rear chassis wall.

FIG. 10D is a perspective view of the power sub-frame 72, which showsthat this in fact forms part of a power sub-assembly 71. Internal walls200 separate three compartments, each for a respective one of the threepower supply units 74. Cables 202 connect standby power and signal linesfrom the power distribution board 190 to a connector 204 for connectionto an alarms module. Cables 206 connect main power and signal lines fromthe power distribution board 190 to various connectors 208, 210, 212 and214. FIG. 10E shows the various connector types 192, 204, 208, 210, 212and 214 and the electrical signal connections thereto.

FIG. 11 is a schematic representation of some of the logic connectionson the power distribution board. For ease of explanation, only thoseconnections relevant for an understanding of the present invention aredescribed.

At the left of FIG. 11, the three connectors 192A, 192B and 192C for thethree power supply units 74A, 74B and 74C are shown. For reasons ofclarity and convenience only those connections relevant for anunderstanding of the present invention as shown. For example, asillustrated with respect to FIG. 10E, the connectors 192 have many pinsand pass many signals via respective lines. However, as not all of theselines are necessary for an understanding of the present invention, andas it would be confusing to illustrate all of the signal pathways on adiagram, only selected pathways are shown in FIG. 11. It is to be notedfrom FIG. 10E, that the power supply units output ground, +3V3,+5V,+12V, −12V and +5V standby potentials as well as control signals such asPSU OK, PSU ON, etc. The +5V standby voltage is used for powering thealarm module 78. The other voltages are for powering the motherboard andother main system components. The various lines could be configuredusing bus bars, wires, printed circuit or thick film conductors asappropriate.

Firstly, the two-of-three circuit 232 will be explained. This circuit ispowered by the +5V standby voltage 231 provided from each of the powersupply units 74. Each of the power supply units outputs a PSU OK signalvia a pin on its respective connector to a corresponding PSU OK line230A, 230B and 230C when the power supply unit is operating correctly.Each of these PSU OK lines 230 is connected to the two-of-three circuit232. This comprises three AND gates 234, 236 and 238, each for comparinga respective pair of the PSU OK signals. The outputs of the AND gatesare supplied to an OR gate 240.

If the output of this OR gate is true, then at least two of the powersupply units 74 are operating correctly, and power can be supplied tothe motherboard of the computer system. This can be achieved by closingthe main power line 245. An output signal 242 could be supplied to agate 244 (for example a power FET) to enable current to pass to themotherboard and other system components. Additionally, or alternatively,a power OK signal 246 for controlling some other form of switchmechanism (not shown).

If alternatively the output of the OR gate 242 is false, then thisindicates less than two of the power supply units 74 are operative. Inthis case power is prevented from being passed to the motherboard 40 ofthe computer system. This can be achieved by interrupting the main powerline 245. An output signal 242 could be supplied to a gate 244 (forexample a power FET) to prevent current being passed to the motherboardand other system components. Additionally, or alternatively, a powerfault signal 246 could be passed to the alarms module and/or forcontrolling some other form of switch mechanism (not shown).

One-of-three power control is effectively provided by the alarms module78 to be described later. However, with reference to FIG. 11, input A/Bsignals 268 and output sense signals 270 are passed to the alarms modulefor standby operation, and control signals 272 could be returned forturning off of a power supply unit, if required.

FIG. 11 further illustrates a protection circuit 256 that is able todetect an overcurrent representative of a current greater than 2*Imax,where Imax is the maximum current that can be output by a power supply,2*Imax being the maximum current which should be required by the systemunit. If a current greater than 2*Imax is detected, this isrepresentative of a fault in the system unit. In accordance with telcorequirements, in such a situation the system should be powered down. Byproviding for overcurrent detection on the power distribution board,where the maximum drawable current should be 2*Imax, it is possible totest for a fault at a lower overall current than if this test were madewithin each power supply unit. If the test were made in each powersupply unit, each power supply unit would need to be tested for anovercurrent in excess of Imax, whereby one would be testing for a totalcurrent drain of 3*Imax. This could lead to faults not being detected ornot detected early enough and the system could incorrectly be drawing upto 3*Imax, which could damage components and traces (tracks).

Thus, as shown in FIG. 11, each of the main power lines (e.g., +12V)250A, 250B and 250C from the power supply units 74A, 74B and 74C,respectively is connected to form a common power supply line 254. Anovercurrent detector 258 detects a current in excess of 2*Imax. If sucha current is detected (for example as a result of a fault represented bythe box 266), then a signal 261 is provided to the connectors 192,A,192B and 192C for shutting down the power supplies 74A, 74B and 74C,respectively. Also, a signal 262 is passed to a switchable shunt 260(e.g., a silicon controlled rectifier (SCR), a Metal Oxide SemiconductorField Effect Transistor (MOSFET), an Insulated Gate Bipolar Transistor(IGBP), etc) to shunt the power supply line 254 to ground. This willcause any energy stored in the power supplies and also in the system(for example as represented by the capacitor 264) to drain to ground,thus protecting the system.

The use of the two-of-three circuit described above means that redundantpower supply operation is provided in that the system can remain poweredeven if one of the three power supply units fails. As only two-of-threepower supply units are needed to power the system the third power supplyunit can be hot swapped while the other two power supply units power thesystem.

FIG. 11 illustrates the location of an alarms card forming the alarmsmodule 78 in the rear of the system unit 10.

FIG. 12 is a functional block diagram for illustrating the alarmsub-system on the alarms module 78. The alarms sub-system provideslights out management or remote management of the system over a serialconnection. The alarms module 78 interfaces with the motherboard throughan EBus edge connector slot 298 (connected to EBus2 as shown in FIG. 8).A PCI-style bracket is attached to one edge of the alarms module (asseen in FIG. 11) and provides the external interfaces at the rear of thechassis 11. Internal interfaces provide connections to the power supplyassembly and to the LED card 80 located at the front panel of the systemunit 10. The alarms module is powered by the standby, or reserve, powersupply. The alarms module only requires power from a single power supplyto remain operable. Accordingly, the alarms module can remain operableeven in a situation where the system has been powered down due to therebeing only one power supply unit operable.

The alarms sub-system comprises a logic device 280 which receives inputs298 from the EBus, inputs 286 from the fans, input 290 from generalpurpose events, input 270 from the power supply unit output rails andinputs 268 from the A and B power inlets. The logic circuit samples, ormultiplexes, the inputs to the microcontroller 296 in response tomultiplex signals from the microcontroller 296. The microcontroller 296processes the sampled (multiplexed) inputs. The microcontroller 296provides power control signals 272 for controlling the power supplyunits, and alarm outputs for the output of alarm signals. Themicrocontroller 296 also outputs power supply unit status signals 304and fault signals 306. The micro controller 296 can further output asystem reset signal 310, when required. Alarm signals to be passed to aremote location can pass via a remote serial connection 112. Diagnosticand remote control signals can be passed from the network via the serialconnection 112 to the microcontroller 296. Control signals can thus beprovided via the remote serial connection over the network for poweringon and powering off the system. Examples of other commands that can besent to the microcontroller via the remote serial connection 112 are toturn alarms off, to reset the monitoring of all failures, to display thestatus of all fans, power supply units, alarms and fault Light EmittingDiodes (LEDs), to display an event log, etc.

The microcontroller is programmed to report any fan failures or changesin power supply units status by means of the LEDs 92 (FIG. 5) on thesystem front and optionally to report the faults via the remote serialconnection 112. The microcontroller 296 is programmed to maintain theevent log that was referenced above.

FIG. 14 illustrates the configuration of the fan control module 66 shownin FIG. 4. The fan control module is subdivided into two halves 66A and66B. One half 66A handles one processor fan 68A and one system fan 70Band the other half 66B handles the other processor fan 68Band the othersystem fan 70B. The fans are connected to the fan control module 66 byrespective power lines 320 so that the fans receive their power via thefan control module. The fan control module receives +12V power via powerlines 324A/B from the power distribution board 190 and supplies voltagesto the fans via the power lines 320 in a controlled manner.

For convenience, tacho (speed) signals from the fans pass via the alarmscontrol module 66. The speed signals are not processed by the fancontrol module, but are instead forwarded via tacho sense 326 to thepower distribution board 190. The power distribution board then routesthe tacho sense signals to the alarms module 78 to form the signals 286shown in FIG. 13. This routing is convenient as it enables simplerwiring looms to be used. Also, when replacing a fan unit, themaintenance engineer only needs to remove a single bundle of wires fromthe fan to the fan control module 66, rather than having to locate anumber of different connectors connected to the fan. The fan controlmodule thus has four fan connectors, each for receiving a connectorconnected to a bundle of wiring from a respective fan, plus a furtherconnector for receiving a connector with a bundle of wires from thepower distribution board.

As shown in FIG. 14, each half 66A/66B of the fan control modulereceives respective power lines 324A/B from the power distributionboard. Each half of the fan control module includes electrical noiseisolation circuitry 340A/B. This electrical noise isolation circuitry325 A/B, which can be of conventional construction, prevents dirty powersignals on the lines 320A/B caused by electrical noise from the fansbeing passed back along the power lines 324A/B and potentiallycontaminating the otherwise clean power supply to the electronics of thesystem unit (e.g., the components on the SCSI bus. The provision ofclean power supply signals in a telco application is important in orderto ensure reliability of operation. Although in the present example thenoise isolation circuitry is located in the fan control module, it couldbe located elsewhere as long as it is effective to isolate the mainpower lines from fan-related electrical noise.

As further shown in FIG. 14, each side 66A/B of the fan control modulecomprises control logic 342A/B which receives a temperature signal froma temperature sensor 344 and adjusts the speed of the fans by adjustingthe voltage supplied thereto in accordance with pre-programmedparameters in order to provide a desired degree of cooling. The controllogic 342A/B can be implemented by an ASIC, a programmable logic array,or any other appropriate programmable logic. Alternatively, it could beimplemented by software running on a microcontroller or microprocessormodule.

It should be noted that the fan control module could be implemented in aunitary manner, rather than being divided into two halves. Although inthe present instance the fan control module is preferably configured ona single circuit board, this need not be the case. Also, although thetemperature sensor is also mounted on the same circuit board, it couldbe mounted elsewhere. Moreover, although it is preferred that a singletemperature sensor is used, with the advantage that the fan speeds ofthe respective fans can be ramped up in parallel in a controlled manner,more than one temperature sensor could be used. Ideally, in this casethey would be located close together and control of the individual fanscould be dependent on individual signals but would more preferably bedependent on a function of some or all of the temperature signals. As afurther feature, the control logic could be provided with different setsof programmed parameters depending on the number of processors presentand could be responsive to the number of processors present.

It will be appreciated that although particular embodiments of theinvention have been described, many modifications/additions and/orsubstitutions may be made within the spirit and scope of the presentinvention. Accordingly, the particular example described is intended tobe illustrative only, and not limitative.

What is claimed is:
 1. A power sub-frame for a system unit, the power sub-frame comprising four walls defining first, second, third and fourth sides of a frame, a fifth, open, side of the frame for receiving a plurality of power supply units for powering the system unit and a power distribution board located at a sixth side of the frame opposite to the open side for making electrical contact to the power supply units, wherein the power distribution board carries a plurality of power rails for supplying different components.
 2. The power sub-frame of claim 1, further comprising internal walls for defining a plurality of compartments, each for receiving a power supply unit.
 3. The power sub-frame of claim 2, comprising two internal walls for defining three compartments.
 4. The power sub-frame of claim 1 comprising formations for securing the power sub-frame in the system unit.
 5. The power sub-frame of claim 4, wherein the formations comprise flanges with holes for receiving retaining screws.
 6. The power sub-frame of claim 1, wherein the power distribution board comprises cabling for connection to components of the system unit.
 7. The power sub-frame of claim 1, wherein the power distribution board comprises power distribution logic.
 8. The power sub-frame of claim 1, comprising metal walls.
 9. The power sub-frame of claim 8, wherein the walls have openings.
 10. A system unit comprising electronic circuitry and a power sub-assembly, the power subassembly being formed by a power sub-frame including four walls defining first, second, third and fourth sides of a rectangular frame, a fifth, open, side of the frame for receiving a plurality of power supply units for powering the system unit and a power distribution board located at a sixth side of the frame opposite to the open side for making electrical contact to the power supply units, wherein the power distribution board comprises a plurality of power rails for supplying different components of the system unit.
 11. The system unit of claim 10, wherein the power sub-frame further comprising internal walls for defining a plurality of compartments, each for receiving a power supply unit.
 12. The system unit of claim 10, wherein the power sub-frame comprises two internal walls for defining three compartments.
 13. The system unit of claim 10, wherein the power sub-frame comprises formations securing the power sub-frame in the system unit.
 14. The system unit of claim 13, wherein the formations comprise flanges with holes for receiving retaining screws that engage with holes in a chassis of the system unit.
 15. The system unit of claim 10, wherein the power distribution board comprises cabling for connection to components of the system unit.
 16. The system unit of claim 10, wherein the power distribution board comprises power distribution logic.
 17. The system unit of claim 10, wherein the power sub-frame comprises metal walls.
 18. The system unit of claim 10, wherein the system unit is a computer system unit including processing circuitry.
 19. The system unit of claim 10, comprising three power supply units.
 20. The computer system of claim 10, wherein the system unit is rack mountable.
 21. A method of assembling a system unit including a plurality of power supply units, the method comprising: providing a sub-assembly forming a power sub-frame, the power sub-frame comprising four walls defining first, second, third and fourth sides of a rectangular frame, a fifth, open, side of the frame for receiving a plurality of power supply units for powering the system unit and a power distribution board located at a sixth side of the frame opposite to the open side for making electrical contact to the power supply units, wherein the power distribution board comprises a plurality of power rails for supplying different components of the system unit; and mounting the power sub-frame sub-assembly in the system unit.
 22. The method of claim 21, comprising securing the power sub-frame sub-assembly in the system unit using respective formations of the power sub-frame and the system unit.
 23. The method of claim 22, wherein the formations comprise flanges on the power sub-frame sub-assembly with holes that cooperate with holes on a chassis of the system unit for receiving retaining screws.
 24. The method of claim 21, comprising connecting cabling of the power sub-frame sub-assembly to components of the system unit.
 25. The method of claim 21, wherein the system unit is a computer system unit including processing circuitry.
 26. The method of claim 21, comprising mounting the system unit in a rack. 